Conventional mounting methods of semiconductor element are described below by referring to the drawings.
(Prior Art 1)
FIG. 16 is a sectional view of mounting a semiconductor element on a circuit board in prior art 1.
In FIG. 16, reference numeral 1 is a semiconductor element, an electrode 2 is formed on the semiconductor element 1, and a protruding bump (metal ball bump) 15 made of gold, copper, aluminum, solder or the like is formed on the electrode 2 by wire bonding method.
Reference numeral 4 is a circuit board made of an insulating substrate, and a copper foil 5 to be used as wiring is formed on this circuit board 4, and a copper-plated external electrode terminal 6 is formed on the circuit board 4. To conduct within the circuit board, a hole 8 formed in the circuit board 4 is filled with conductive paste 7.
Reference numeral 22 is a conductive paste (conductive adhesive) having conductive powder of silver, gold, nickel, carbon or the like dispersed uniformly on phenol or epoxy resin. The external electrode terminal 6 of the circuit board 4 and the electrode 2 of the semiconductor element 1 are electrically connected with each other through the protruding bump 15. The space between the circuit board 4 and semiconductor element 1 is filled with epoxy resin 20.
A mounting method of thus constituted semiconductor device is described below.
The conductive paste 22 is transferred on the protruding bump 15 formed on each electrode 2 of the semiconductor element 1 by transfer method, it is mounted so that the protruding bump 15 may coincide with the external electrode terminal 6 of the circuit board 4 to be mounted, and then it is heated to cure the conductive paste 22. In this way, the electrode 2 of the semiconductor element 1 and the external electrode terminal 6 of the circuit board 4 are electrically connected. After the connection, the space between the semiconductor element 1 and circuit board 4 is filled with the epoxy resin 20, and by making use of the shrinking force of its curing, continuous contact of the conductive powder of the conductive paste 22 is obtained, so that electrical and mechanical reliability is assured.
(Prior Art 2)
FIG. 17 is a sectional view of mounting a semiconductor element on a circuit board in prior art 2. Same parts as in the constitution in FIG. 16 are identified with same reference numerals and their explanation is omitted.
In FIG. 17, reference numeral 23 is a metal bump formed on an electrode 2 by electric plating method, and the metal bump 23 is, for example, plated with copper and further plated with gold 24. Reference numeral 25 is an external electrode terminal, and 16 is a passivation film for protecting the active surface of the semiconductor element 1.
A mounting method of thus constituted semiconductor device is described below.
The conductive paste 22 is transferred on the metal bump 23 formed on each electrode 2 of the semiconductor element 1 by transfer method, it is mounted so that the metal bump 23 may coincide with the external electrode terminal 25 of the circuit board 4 to be mounted, and then it is heated to cure the conductive paste 22. In this way, the electrode 2 of the semiconductor element 1 and the external electrode terminal 25 of the circuit board 4 are electrically connected. After the connection, the space between the semiconductor element 1 and circuit board 4 is filled with the epoxy resin 20, and by making use of the shrinking force of its curing, continuous contact of the conductive powder of the conductive paste 22 is obtained, so that electrical and mechanical reliability is assured.
(Prior Art 3)
FIG. 18 is a sectional view of mounting a semiconductor element on a circuit board in prior art 3. Same parts as in the constitution in FIG. 16 and FIG. 17 are identified with same reference numerals and their explanation is omitted.
In FIG. 18, reference numeral 3 is a protruding bump (protruding electrode) formed on an electrode 2 by plating method, and 26 is an insulating adhesive film, and conductive particles 27 of nickel, solder, carbon, or the like are uniformly dispersed in the insulating adhesive film 26.
A mounting method of thus constituted semiconductor device is described below.
The insulating adhesive film 26 is positioned between the semiconductor element 1 and external electrode terminal 25 of the circuit board 4, and heated and pressurized simultaneously. As a result, the adhesive film 26 is melted to flow into the space in the electrode 25, the conductive particles 27 are fixed and held by the protruding pump 3 and external electrode terminal 25, so that the protruding bump 3 and external electrode terminal 25 conduct. In the space, on the other hand, the conductive particles 27 remain dispersed in the adhesive, and the insulation is maintained. The adhesive film 26 is cured when cooled, and the semiconductor element 1 and circuit board 4 are fixed, and the connection reliability is assured. the mounting method of semiconductor element in prior art 1 (or prior art 2), however, as shown in FIG. 19, when transferring the conductive paste film 28 on the protruding bump 15 by transfer method and joining the bump 15 to the external electrode 6 of the circuit board 4, it is hard to control the amount of the conductive paste 22 to be transferred, and if the amount of the paste 22 is slightly excessive, a short circuit 30 may be formed in the electrode 2 by the conductive paste 22. Or if the circuit board 4 is slightly warped, the electrode 2 of the semiconductor element 1 and the external electrode terminal 6 of the circuit board 4 do not contact with each other through the conductive paste 22, and it is electrically open between the electrode 2 and external electrode terminal 6.
Further, as shown in FIG. 20, when filling the space between the semiconductor element 1 and circuit board 4 with epoxy resin 20, the epoxy resin 20 contained in a syringe 31 is injected from the periphery of the semiconductor element 1, and it takes more than 10 minutes to inject, and it was a bottleneck for shortening the cycle time of production line of semiconductor element 1.
In the mounting method of semiconductor element in prior art 3, since conduction is achieved by fixing and holding the conductive particles 27 between the electrode 2 of the semiconductor element 1 and electrode 25 of the circuit board 4, if the circuit board 4 is slightly warped or curved A as shown in FIG. 21, the conductive particles 27 remain dispersed in the adhesive 26, and the protruding bump 3 of the semiconductor element 1 and the electrode 25 of the circuit board 4 do not contact with each other, and hence it is electrically open between the protruding bump 3 and electrode 25. In the mounting method of prior art 3, incidentally, it is applied to a glass substrate which is hardly warped or curved, and is not applied to resin substrate.
It is hence an object of the invention to present a mounting method of semiconductor element free from occurrence of defects such as short circuit or open state between electrodes, capable of mounting at high electric reliability, curtailing the time substantially in the sealing process, and shortening the cycle time of semiconductor production line.